I would drop the raid controller and just use the onboard controller. The fake raid that that controller provides isn't going to give you a performance benefit. Use the extra cash to get a better cpu/vid card.
Note how he used a triple core cpu, which is better suited to gaming. An aftermarket cooler was added and it was overclocked to optimize performance for no extra price.
I know you are trying to save money on case and PSU, but Logisys does not make good power supplies - Antec, on the other hand, has a good reputation, and even though the one in the marathon was cheap, it should have an adequate quality and not risk frying your computer.
1 TB of disk dirve will probably not add much to the performance of the machine, even if it is in RAID0. consider a single 500 GB, or even a 320 GB drive, since your games will only consume a small percentage of that capacity. You can always upgrade that easily later on, as drive prices continue to drop.
The 5770 Video card is a good card, and will play almost any game at medium quality or better. If you have a little bit more money, think about an upgrade to a motherboard that has two PCIe slots with at least 8 X 8 bandwidth, then add a second 5770 in crossfire. That will make your gaming machine really stand out!